1. Field of the Invention
The present invention relates to a deinterleaver for deinterleaving an interleaved data sequence, and in particular to a deinterleaver required for a code division multiple access (CDMA) terminal unit operating in conformity with the U.S. IS-95 Standard.
2. Description of the Related Art
In communication systems, there possibly occur consecutive errors in communication data depending on environments of data transmission paths and the like to resultantly invalidate the advantageous effect of the random-error-correcting coding. In such a situation, there are commonly achieved the following operations. Namely, to convert data errors successively occurred during transmission into random data errors, the order of transmission data to be transmitted is rearranged to a predetermined random order and then the transmission data are sent from a transmitter. In a receiver, the order of reception data is rearranged in the correct order or the original order. An apparatus to rearrange the order of the transmission data to the predetermined random order is called an interleaver, and an apparatus to rearrange the order of the reception data to the correct order is called a deinterleaver.
A conventional deinterleaver includes, as shown in FIG. 1, a first storage unit 110, a data latching unit 120, a second storage unit 130, and an addressing unit 140 including a binary counting unit 141 and a third storage unit 142.
Reception data are sequentially stored in the first storage unit 110 beginning at address "0". The binary counting unit 141 of the addressing unit 140 counts from the initial count value "0" to the number of the reception data stored in the first storage unit 110, and produces an output signal corresponding to the count value. The output signal is outputted to the first and third storage units 140 and 142 as a read addressing signal. Therefore, the reception data stored in the first storage unit 110 are sequentially read out therefrom in response to the read addressing signal from the binary counting unit 141 beginning at address "0". The reception data read out from the first storage unit 110 are temporarily held in the data latching unit 120.
In the third storage unit 142 of the addressing unit 140, the numbers representing the correct order of the reception data are stored beginning at address "0". The numbers are sequentially read out from the third storage unit 142 in response to the read addressing signal from the binary counting unit 141 beginning at the number stored at address "0". The number read out from the third storage unit 142 is outputted to the second storage unit 130 as a write addressing signal.
In the second storage unit 130, the reception data temporarily held in the data latching unit 120 are stored at an address specified by the write addressing signal from the third storage unit 142. Resultantly, the reception data are sequentially stored in the second storage unit 130 in the correct order beginning at address "0".
That is, in the deinterleaver shown in FIG. 1, the reception data are sequentially read out from the first storage unit 110 in the order of reception. When the reception data read out from the first storage unit 110 are written to the second storage unit 130, the write address of the second storage unit 130 is modified. Thereby, the order of the reception data is rearranged to the order before the interleaving operation.
However, since the conventional deinterleaver requires a memory having a relatively large storage capacity as the third storage unit 142 which is used for storing the numbers representing the correct order of the reception data as the write address information of the second storage unit 130, the hardware area and power consumption are disadvantageously increased. Consequently, such a deinterleaver cannot be suitably installed in a reception apparatus such as a mobile communication terminal equipment of which the size and power consumption are required to be minimized.